Luminous stretch panel

ABSTRACT

AN IMPROVED PANEL STRUCTURE FOR LUMINOUS CEILINGS IN WHICH A THIN TRANSLUCENT FILM IS FORMED ABOUT AN EXPANDED CELLULAR FRAME IN EXTENSION ACROSS THE OPENING THERE THROUGH AND IN TENSION THEREUPON.

Feb. 2, 1971 w c, NANNY ETAL 3,560,317

- LUMINOUS STRETCH PANEL Original Filed April 21, 1.966

United States Patent O 3,560,317 LUMINOUS STRETCH PANEL William C. Nanny, San Francisco, and Russell D. Squire,

San Mateo, Calif., assignors to Residential Lighting Sales Company, San Francisco, Calif., a partnership Continuation of application Ser. No. 544,287, Apr. 21,

1966. This application June 24, 1969, Ser. No. 836,120 Int. Cl. 1832b 1/04, 3/02 US. Cl. 161-43 7 Claims ABSTRACT OF THE DISCLOSURE An improved panel structure for luminous ceilings in which a thin translucent film is formed about an expanded cellular frame in extension across the opening therethrough and in tension thereupon.

This is a continuation of our copending US. patent application Ser. No. 544,287, filed in the U. S. Patent Olfice on Apr. 21, 1966 and entitled Luminous Stretch Panel now abandoned.

BACKGROUND OF THE INVENTION In the field of illumination there have been developed luminous ceilings and walls which actually comprise translucent panels or diffusers covering lighting fixtures such as fluorescent tubes or the like. Particularly with respect to luminous ceilings, it is conventional to employ lightweight metal structures to support contiguous panels of translucent material beneath lighting fixtures affixed to the ceiling itself. This, then, forms a false luminous ceiling beneath the fixtures so that light is rather uniformly distributed throughout a room or the like, and relatively pleasing appearances may be achieved. Support of the luminous ceiling is commonly accomplished by the utilization of T-bars which generally comprise elongated aluminum strips with hangers extending upwardly therefrom into engagement with the ceiling structure; and, these strips are separated predetermined distances to form modules into which light diffusers may be placed from above. Translucent panels or light diffusers may be formed of glass, but are more commonly formed of some type of light-weight plastic to minimize weight and cost.

There are various requirements for luminous panels that are generally applicable, and thus, for example, such panels should, in general, be relatively light in weight, so as to be easily carried by the support structure and should transmit a maximum amount of light emitted from the fixtures thereabove while diffusing the light therethrough. Luminous panels should also have sufficient structural rigidity or strength to retain their original or normal shape without sagging during use and should provide a pleasing appearance. For many applications it is also desirable for luminous panels to have good acoustical properties.

With regard to panels employed in luminous ceilings there is a further and quite strict requirement that they be self-extinguishing insofar as fire is concerned. There are general published Underwriters definitions and requirements in this connection and, commonly, a luminous ceiling is defined as one in which over one third of the ceiling area has light sources therebehind, and in practice, such ceilings are normally comprised of a large number of contiguous panels mounted in the manner noted above. Panels adapted for use in luminous ceilings must not char or burn at greater than a prescribed rate, normally defined in terms of the tunnel test and are considered to be properly self-extinguishing when graded at 25 or less in the tunnel test. As a practical matter, the material polyvinyl chloride will pass this test if the thickness thereof is sufiiciently limited.

Patented Feb. 2, 1971 Conventional luminous ceilings are comprised of a large number of relatively small luminous panels. The reason for the limited size of the individual panels is the necessity of making the material thereof quite thin in order to meet the self-extinguishing criteria noted above, and at the same time to provide sufficient structural strength that the panels do not sag. Although it may be postulated that larger panels could be made by employing a thicker material and, in fact, such is done for individual fixtures, it is not possible to take this approach for luminous ceilings, for the reasons noted above.

Luminous ceilings have to date been limited to a large plurality of relatively small luminous panels. This is highly disadvantageous from a variety of viewpoints related both to structural and architectural criteria. Of substantial importance in this respect is the understandable desire of architects and designers to employ larger panels to eliminate the cut up or busy effect projecting by presently available small panels, particularly for large expanses of luminous ceilings. The present invention provides a solution to the above-noted problems in the presentation of an entirely new type of luminous panel for luminous ceilings, wherein much larger panels are provided and the capability of architecturally pleasing configurations is incorporated.

SUMMARY OF THE INVENTION The present invention is comprised as a very lightweight frame formed of expanded cellular material, such as polystyrene, having the outer edges thereof inclined inwardly toward the back of the frame. Across this frame is stretched a thin film of translucent plastic which is vacuum-formed about the edges of the frame, including the above-noted inclined portions thereof, so as to permanently lock the film and frame together with the film in tension across the opening in the frame. Although neither the expanded cellular frame nor the thin film individually exhibit much in the way of structural strength, the combination thereof, as set forth above, exhibits remarkable structural rigidity. It is thus possible, in accordance with the present invention, to form luminous stretch panels for luminous ceilings in much larger sizes than previously possible. The luminous panel of the present invention meets all Underwriters requirements regarding the abovenoted self-extinguishing property in connection with fire or flame, and yet exhibits sufficient structural strength to withstand sagging when formed in large panels mounted in a luminous ceiling. By those knowledgeable in the art, the luminous stretch panel of the present invention has been termed a new generation in lighting panels, for it has opened up hitherto unavailable areas of luminous ceiling development, particularly insofar as architectural design is concerned.

DESCRIPTION OF FIGURES The present invention is illustrated as to a particular preferred embodiment thereof and a method of manufacture in the accompanying drawings, wherein:

FIG. 1 is a plan view of a preferred embodiment of the luminous stretch panel of the present invention;

FIG. 2 is a side elevational view of the panel of FIG. 1;

FIG. 3 is a partial transverse sectional view taken in plane 33 of FIG. 2; and

FIG. 4 is a schematic illustration of a process for manufacturing the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT Considering now the illustrated embodiment of the present invention as illustrated in FIGS. 1 to 3 and referring thereto, it will be seen that there is provided a luminous panel 11, generally comprised of a four-sided frame 12, with a central opening 13, therethrough. The cross-sectional configuration of this frame 12 is susceptible of wide variation but includes side surfaces that are inclined or stepped inwardly toward the back of the frame. The frame may, as illustrated in FIG. 3, include an outer edge surface 14 with a stepped back surface defined, for example, by a flat, rear surface 16 with an outwardly tapering peripheral surface 17 and flat shoulder portion 18 extending to the edge surface 14. The purpose of this particular rear surface configuration is described below. The front of the frame includes a flat front surface 21 with a recessed shoulder 22 thereabout extending to the edge surface 14. The front of the frame also includes an inner surface 23 which, in cross section, may be slightly curved as illustrated in FIG. 3. As shown in plan view, the frame may, for example, exhibit a sculptured effect wherein the front surface 21 has a minimum dimension at the center of each frame side and tapers to a wider dimension adjacent the frame corners. Although this particular configuration has a pleasing appearance, it is, of course, possible to vary it considerably with the only limitation that the outer dimensions and configuration of the frame be modular to the extent that they are adapted to conventional mounitng. Such mountting is schematically illustrated in FIG. 2 by the dotted T- bars 31 and it will be seen that the shoulder 22 about the periphery of the frame is adapted to rest upon adjacent T-bars 31, so as to support the panel with the front face thereof disposed downwardly.

In addition to the frame portion 12 of the luminous panel, the present invention also includes a film or sheet 41 extending across the frame opening, and about the sides of the frame. More particularly, the film 41 extends as a sheet 42 across the frame opening at the back thereof and along the inner inclined frame surfaces 23 across the frame front 22 and about the frame sides. Particularly as shown in FIG. 3, the configuration of this film 41 is clearly illustrated as being conformed to the inner surface, front surface and outer side surface of the frame, including the shoulder 22 and inwardly inclined outer frame surface 14. This film is tightly fitted to the frame as, for example, in the manner described below, and extends in tension as the sheet 42 across the frame opening.

The present invention provides a particular combination of light-weight frame and tensioned film or sheet permanently attached thereto. In this manner there is achieved results hitherto unavailable with luminous panels. The unit may, for example, be likened to a drum head, wherein the skin is maintained in tension across a tensioning member, for in this instance the frame comprises a tensioning member carrying the sheet or film in permanent attachment thereto. In this manner, the present invention provides for extending the thin translucent sheet 42 across a substantial area without possibility of the sheet sagging during use.

Further to specific requirements of luminous panels, it is noted again that a translucent panel adapted for utilization in a true luminous ceiling requires the utilization of a material which is termed self-extinguishing so far as fire or flame is concerned. The majority of available materials do not meet this criteria. One material approved by Underwriters testing which does satisfy this requirement is a sheet of polyvinyl chloride having a limited thickness. In accordance with the present invention, the thickness of the film 41 is 0.013 inch and no greater than 0.015 inch. It will, however, be appreciated that a film or sheet of the thickness is not normally selfsupporting over any substantial distance and will, in fact, sag under normal usage. By the particular combination of the above-noted thin film or sheet of polyvinyl chloride with a light-weight frame formed of expanded polystyrene in a manner which firmly locks the sheet or film to the frame, there is achieved a unitary structure herein which is highly advantageous as a luminous panel for luminous ceilings. The translucent sheet is attached to the frame in tension and is furthermore folded back about the outer frame surfaces or edges onto a surface that is inclined toward the back of the frame, so that a true locking action is achieved and under no circumstances can the sheet or film come loose from the frame. This joinder of film and frame may be accomplished by vacuum bonding techniques, as described below. It is, however, to be particularly noted that attainment of the objects of extending the area of a luminous panel cannot be achieved by merely employing a thicker sheet or film, for then the structure would not be self-extinguishing.

Further to the materials of the present invention and, as described in some detail below, the polyvinyl chloride film or sheet is heated to a softening temperature in order to form it about the frame, and yet the softening temperature of this particular material is about 20 below the softening temperature of expanded polystyrene. While it may be postulated that alternative plastic films could be employed with the frame of this invention, it is noted that same do not pass the Underwriters tunnel test so as to be self-extinguishing. Consequently, such an approach is not practical. Referring further to polyvinyl chloride, it is noted that a sheet of this material having 7 a thickness of 0.125 inch will support itself without sagging. However, the present invention provides for utilization of a film only about this thickness. A practical luminous panel formed in accordance with the present invention employs a frame of expanded polystyrene weighing about three ounces and supporting about eight ounces of polyvinyl chloride film. The frame is almost entirely contained by the film and exhibits remarkable strength under these conditions to maintain the film in tension across the opening of the frame. Such a panel may be formed in sizes from 2 feet by 2 feet to sizes 2 feet by 4 feet or 3 feet by 3 feet. Luminous panels of these larger sizes for luminous ceilings are unknown in the art.

In addition to the foregoing portions of the present invention, there may also be provided a top element or panel 46 formed of transparent or translucent sheet material, and having a stepped periphery, as illustrated in FIG. 3, to rest atop the frame in horizontal position. This upper element has a flat central portion 47 thereof, displaced upwardly from the top or rear surface of the frame so as to define an air space between same and the panel skin 42. The provision of such an upper element is known in the art and serves to provide the advantage of acoustical insulation, as well as improving the optical properties of the panel. In common with prior art panels, the present invention provides for masking the presence of any small object, such as a piece of dirt or the like that might, inadvertently, fall upon the upper surface of the panel. By the utilization of two spaced, light transmitting elements 42 and 47, the lower element is protected from dirt or the like, and the double diffusion of light prevents a darkened image of an object upon the upper surface 47 from being visible through the overall panel. It is possible to provide the upper element 46 as a transparent element and the lower sheet, or film 42, as a translucent element, although under certain circumstances this arrangement may be reversed.

This top panel 46 is also formed of the same material as the film or sheet 41 of the luminous panel of the invention. It does, in fact, have substantially the same thickness as the film 41 so that then the total thickness of the two sheets extending across the opening of the frame is no greater than 0.030 inch and testing by the Underwriters Laboratory has established that polyvinyl chloride with this thickness is, indeed, self-extinguishing, so that the panel has been approved for luminous ceilings.

Considering now the method of manufacture of the present invention, reference is made to FIG. 4 illustrating steps in the manufacturing process. Initially the frame itself is formed in a mold by conventional means and, as noted above, is comprised of a cellular structure such as expanded cellular polystyrene so that the cells thereof are closed. The density of the frame itself may be varied as desired and may, for example, have a density of 1.75 lbs./ ft. However, it is emphasized that very low density materials may be employed for the frame, in order to minimize cost and weight thereof. The frame structure alone has a rough, open cellular surface, almost entirely unsuited to general usage because of the perviousness thereof to dust and dirt, and because of the fragile nature of such surface which tends to flake off with use and to be readily dented or punctured. The process, in brief, comprises vacuum bonding of the sheet 41 onto the frame 12. This is accomplished by initially heating the sheet to softening temperature and, then lowering the sheet onto the frame fixed in position and sucking the sheet into intimate and contiguous contact with the frame surface. The sheet 41 is then intimately contacted with the frame and extended in tension across the frame opening. Outside edges of the sheet are then trimmed from the frame, and the unit is cooled as a finished product of manufacture.

Considering now the individual steps of a method of forming the present invention in somewhat greater detail, in FIG. 4 there is illustrated the positioning of a frame 12 upon a fixed bed 51 by means of frame rails 52,

so that the frame is fixed in position against lateral movement. It will be seen that the frame is disposed with the backside 16 thereof resting upon the upper surface of the bed 51 and the frame rails 52 engaging the tapered side 17 of the frame. The sheet of polyvinyl chloride of abovenoted thickness is laid upon an upper movable carriage 53, having a central opening of greater dimension than the dimensions of the frame 12. The sheet is clamped onto the carriage by upper carriage bars 54 about the periphery of the sheet, so that the sheet is then held in position on this carriage. As shown in FIG. 4, the sheet is positioned immediately above the bed 51 and frame thereon, and in this position is heated from above, as indicated by the arrows 56. This heating may be accomplished by electrical heaters 57 movable into close relationship immediately above the sheet. In practice, it has been found that as the sheet is heated, it commences to sag or wrinkle and, with polyvinyl chloride, additional heating then tightens the sheet. The sheet 41 may be heated to a temperature of the order of 165 F. but at any rate is only heated to softening temperature.

When the sheet is appropriately heated it is immediately lowered onto the frame by moving the carriage 53 downwardly onto the bed 51. Appropriate seals are provided on the underside of the carriage 53 and upper surface of the bed 51 about the frame mounting so as to define a vacuum-tight chamber above the bed and beneath the sheet when the carriage is fully lowered. A vacuum is drawn through the bed, as indicated by the arrows 61 in FIG. 4, and for this purpose there are provided a plurality of perforations 62 through the bed about the interior of the frame immediately adjacent the inner frame edge. There are also provided an additional plurality of openings through the bed, as shown at 63, immediately exteriorly of the frame rails 52. As the softened sheet is rapidly lowered onto the frame with the carriage in sealing relationship with the bed, vacuum is drawn through the openings 62 and 63 as by automatic actuation of a valve 64, so as to suck the softened sheet onto the frame. A very substantial vacuum is employed, as of the order of 22" of mercury, so that a large force is applied to the sheet 41 to very forcibly contact the sheet with the exposed frame surfaces.

In order to insure a close bonding of the sheet to all front and side surfaces of the frame, there are provided a plurality of minute passages 66, extending from the back surface 18 of the frame to the inner edge of the front shoulder 22 about the frame periphery. As the vacuum is drawn through the bed, it will be then drawn through these passages 66 so as to suck the sheet into the curvature of the shoulder 22 onto the frame, as shown in FIG.

3. Of course, the vacuum through the opening 62 in the bed draws the central portion of the sheet downwardly to bond it against the inner edges 23 of the frame and to leave the sheet in extension across the frame opening. The sheet does not adhere to the bed itself, but it is drawn about the outer edge surface 14 of the frame and, of course, it will be appreciated that the sheet is stretched in this bonding operation so that some portions of the sheet may actually have a lesser thickness than other portions, but in any case, it is tensioned against the frame and permanently attached thereto.

The entire operation, or process of manufacture, briefly described above requires only a few seconds and it produces the structure shown in FIGS. 2 and 3, but with some edge projection of the sheet which is subsequently trimmed about the frame edge at the juncture of surfaces 14 and 18 thereof. This trimming may be accomplished either manually or automatically, as desired. A relatively instantaneous bonding is accomplished, and the locking bars 54 of the carriage are then released to free the sheet from the carriage and the carriage is then raised back into its upper position, leaving the sheet bonded as a film onto the front surfaces of the frame and extending as a sheet 42 across the internal frame opening. There are also various additional and optional steps in the process of manufacture, such as, for example, initial coloring of the frame itself, as by dipping same in a permanent dye to achieve desirable appearances for particular applications. Also, it is possible to initially color or coat, as by metalizing, a peripheral portion of the sheet 41 forming the film thereof attached to the frame, while the central sheet portion 42 remains in the original condition. It is to be appreciated that coloring of metalizing of the frame portion of the panel, by applying either a color or metallic coating to the skin upon the frame, requires a careful placement of the same u on this skin, for stretching of the film occurs during application to the cellular frame member. Consequently, care must be taken in registry of sheet and frame during processing when this is to be accomplished It is further noted that an identity of appearance between the exposed portions of the hanging structure, or T-bars 31, and the frame portion of the panel may be accomplished in the above-noted manner. Thus, provision of a metallic-appearing frame of the same appearance as the undersurface of the T-bars 31 provides a highly advantageous visual appearance to a completed ceiling wherein it is almost impossible to identify the presence of any hangers. It is furthermore possible, in accordance with the present invention, to provide for some other type of coating upon the film and, likewise, upon the undersurface of the hanging members, such as flocking, for example. This, again, provides for visual blending together of the hanger and panel frame.

With regard to the structure of the present invention, it is noted that there has been described above a process for tightly engaging film and frame in the manufacture of a luminous panel in accordance with the present invention. In accordance with the present invention, an expanded polystyrene is, at least, partly covered with a relatively tough plastic skin in tension, by vacuum bonding so as to produce a resultant structure having properties greatly superior to the individual properties of the materials combined, and exhibiting remarkable structural rigidity in view of the limited strengths of the components. It is furthermore to be noted that the present invention provides for maintenance of dimensional stability which is highly important in various applications of the present invention. By maintenance of the cellular material in fixed position during vacuum bonding, the resultant dimensions of the composite unit are maintained within very close limits to the original dimensions of the object formed of the cellular material. Additionally, the tensioned nature of the film 41 upon the cellular element 12 adds to the structural strength of the resultant panel formed in accordance with this invention. It is emphasized at this point that the materials employed in the present invention are quite low in cost and, furthermore, that the process of fabrication is quite simple and rapid, so as to highly recommend the invention to industrial application.

Although the present invention has been described above in connection with a particular preferred embodiment thereof and the particular steps of the process of manufacture, it is not intended to limit the invention to the exact terminology of this description or details of illustration. Reference is made to the appended claims for a precise delineation of the true scope of the present invention.

We claim:

1. An improved luminous stretch panel comprising a frame element of foamed cellular material having a central opening therethrough and exterior sides inclined inwardly toward the back from a front surface thereof, and a thin plastic sheet of polyvinyl chloride vacuum formed over said front surface and sides of said frame element across the central opening therethrough to provide a structurally strong panel with said sheet in tension across the frame opening.

2. The panel of claim 1 further defined by said frame element comprising a low density expanded polystyrene.

3. The panel of claim 2 wherein said sheet has a maximum thickness of 0.015 inch.

4. The panel of claim 2 further defined by the frame and the sheet having respective weights in the ratio of the order of 8:3.

5. The panel of claim 1 further defined by said frame having curved inner surfaces with a maximum thickness at the corners.

6. The panel of claim 1 further defined by said frame having a shoulder formed about the exterior sides facing the front thereof ahead of said inclined surfaces for mounting of the panel.

7. The panel of claim 1 further defined by said film extending across the back of the frame opening between the interior frame surfaces.

References Cited UNITED STATES PATENTS 3,257,353 6/1966 Eagleton 264-92X 3,382,134 5/1968 Powell 161-43X FOREIGN PATENTS 1,298,849 6/1962 France 156-285 ROBERT F. BURNETT, Primary Examiner R. O. LINKER, 111., Assistant Examiner US. Cl. X.R.

l6144,119,149,16l;24051.1l 

